This invention relates generally to concrete reinforcing steel construction and, more specifically, to the efficient prefabrication and non-structural welding of rebar panels for use in concrete structures. This invention further relates to the fabrication of welded rebar panels on site as well as off site, thereby reducing the cost associated with time, material and labor.
Currently, rebar panels are constructed by wire tying, mechanical couplers, and occasionally by a combination of welding and wire tying. All of these processes are costly because they are labor intensive and time consuming. Further, inherent weaknesses within each method limits the size and shape of panel that can be produced, thereby increasing the steps and thus costs in the overall construction process. As a result, conventional reinforcement steel bars (rebar) assembly methods require more steps with increased costs, resulting in the construction of structurally compromised rebar panels.
Tie wire constructed rebar panels often structurally fail for several reasons. Firstly, the connection resulting from the tying process is subject to human inconsistencies. For example, the tie wire connection is only as strong as the individual person making the tie. Thus, structural inconsistencies often exist in panels where more than one person is constructing a panel, or a single person becomes fatigued while doing so.
Even if tied correctly, tied rebar connections severely limit panel size due to wire strength and overall rebar intersection rigidity. Typically, the panels are assembled and tied with the assembly laid out on the ground near the job site. Upon completion of the tying process, a crane or other machine is used to place the panel in the concrete form. Wire tied panels are often incapable of supporting the panel""s weight during their placement, often yielding a displacement of the tied rebar members known as xe2x80x9craking.xe2x80x9d As the spacing of the rebar must be made within the tolerances specified by the engineer, the displaced rebar must be retied in its specified location increasing labor costs.
Not too different from the tied rebar panels are panels constructed with mechanical rebar couplers. Here, a great variety of mechanical couplers are applied to intersections of the rebar panel in place of wire ties. The couplers are more time consuming to use than the wire tie method discussed above. Generally, however, a more consistent rebar connection is attained when using the mechanical coupler over the tie wire panel construction technique. Thus, when the mechanical coupling is done properly a more consistent panel construction is achieved. However, panels constructed with mechanical couplers are very costly with regards to the multiple steps required to assemble them and the price of the couplers themselves.
Finally, attempts have been made to produce a welded rebar panel. Historically, these attempts have yielded a sub-standard product. All prior welding techniques have not achieved metallurgical properties meeting the requirements for reinforced concrete. Rebar in concrete is designed to support tensile loads; therefore, welds must not compromise the ability of the steel to support such loading. Consequently, a rebar panel constructed with welds not having appropriate metallurgical properties is not desirable and may increase the likelihood of a structural failure.
The present invention is directed to a system and method for the construction of weld-stabilized rebar panels that overcomes the above-mentioned problems.
The present invention comprises a system for the construction of weld-stabilized rebar panels using a plurality of spot fusion welds made by a unique gas metal arc welding (GMAW) process. The system and method includes rapidly welding rebar sections using GMAW to obtain a fusion weld joint. The system includes a rebar shear used to cut the rebar to predetermined lengths, a rebar bender used to impart required curvature to the rebar, a welding jig used to align the rebar in the desired rebar panel configuration, a rebar welder, preferably a gas metal arc welder, a power source, and one or more rolling tables facilitating the movement of the rebar from the rebar shear to the rebar bender and ultimately to the welding jig. In operation, the rebar starts at the rebar shear, where the rebar is cut, as necessary, to predetermined lengths. The rebar then travels along the rolling tables to rebar bender, where any required curvature is imparted to the rebar. The rebar is then forwarded along rolling table to the welding jig, where is comes to a stop aligned within the jig to facilitate intersection with other rebar in the panel assembly. Once the rebar is properly aligned in the welding jig, the rebar welder, powered by the power source, is used to fusion weld the rebar intersections.
Specific settings are used on the welder and the power source in order to achieve a flare bevel groove weld that meets the grade A706 requirements. The use of shielding gas in the method contains not only heat, but also helps create the fusion between the rebar and consumable electrode of the welder without causing any carbon breakdown in the heat-affected zone of the rebar, thus maintaining the rebar ductility and the specific advantages of the present invention.